Maternal diet has been shown to impact fetal development across a variety of species. Given the reported effects of omega-3 long-chain polyunsaturated fatty acid (n-3 LCPUFA) supplementation on health across species, it was hypothesized that supplementation of algal-based n-3 LCPUFA to mares around conception would alter the maternal uterine environment and modify gene expression in early conceptuses. Nonlactating, light horse mares were supplemented with concentrate (n = 6) or an isocaloric diet containing 0.06 g/kg body weight n-3 LCPUFA (primarily docosahexaenoic acid [DHA], n = 7) at least 60 days before first sample collection. Four consecutive ovulatory cycles were monitored. Uterine endometrial samples were obtained 12.5 days postovulation from cycles 1 (uninseminated), 3, and 4 (bred to a common stallion); embryos were flushed from cycles 3 and 4. Biopsies from supplemented mares were greater in DHA and total omega-3 fatty acid concentrations ( P PTGFS and reduced IL6 gene expression ( P PTGES ( P = .05), PTGFS ( P = .03), and SLCO2A1 ( P = .01), while supplemented barren mares exhibited lower PTGFS ( P = .05) and IL6 ( P GATA3 , GATA4 , GATA6, TFAP2A , ELF3 ) was greater ( P
